Antimicrobial anodized aluminum and related method

ABSTRACT

An anodized aluminum product in continuous web or sheet form, which is heat sealed and coated with an antimicrobial composition. The antimicrobial coating can be bound to surface of the anodic layer and can comprise a network of cross-linked organo-silane molecules that are also covalently bound to the surface of the anodic layer. A process also is provided including: forming an anodic layer on the surface of an aluminum substrate; heat sealing the anodic layer; preheating the web or sheet to a range from about 140° F. to about 200° F.; applying an antimicrobial composition at an application rate sufficient for the composition to at least begin binding to the surface of and form an antimicrobial coating over the anodic layer; and post heating the coated anodized antimicrobial web or sheet to a range from about 140° F. to about 200° F. to further bind the composition to the cure the antimicrobial coating.

This application claims priority to U.S. Provisional Application Ser.No. 61/027,505 that was filed on Feb. 11, 2008 and is incorporated byreference herein.

BACKGROUND

The present disclosure relates to a continuous web or sheet of anodizedaluminum including an improved coating and a method for manufacturingthe same.

Anodized aluminum is used in a variety of architectural applications.For example, due to its corrosion and weather resistance, anodizedaluminum sheets are used on building exteriors. Anodized aluminum sheetsalso are used in interior architectural applications. Interiorarchitectural components such as walls, back splashes, partitions, doorknobs and table tops can be manufactured from sheets of anodizedaluminum.

A problem with anodized aluminum sheets is that the surfaces of thesheets are highly hydrophilic. Therefore, water-born microbes andpathogens frequently become joined with the architectural anodizedaluminum sheets. This can become problematic because installed interiorarchitectural sheets are touched or contacted by many different people.In cases where the anodized aluminum sheet is infrequently washed, andwhere microbes and pathogens are given the opportunity to grow on thesurface of the anodized aluminum, the anodized aluminum sheet can becomea transfer agent for those microbes and pathogens. This can lead to anunnecessary health hazard.

SUMMARY

The aforementioned problems are overcome by an anodized aluminum productin continuous web or sheet form, which is heat sealed and coated with anantimicrobial composition.

In one embodiment, the antimicrobial composition is organo-silane based.Optionally the organo-silane is3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride.

The present disclosure also provides a method for producing anantimicrobial anodized aluminum product in continuous web or sheet formincluding: forming an anodic layer on the surface of an aluminumsubstrate by anodically coating an aluminum core in an electrolytesolution; heat sealing the anodic layer with a heated solution of water;preheating the web or sheet to a range from about 140° F. to about 200°F.; applying an antimicrobial composition at an application ratesufficient for the composition to at least begin binding to the surfaceof and form an antimicrobial coating over the anodic layer; and postheating the coated anodized antimicrobial web or sheet to a range fromabout 140° F. to about 200° F. to further bind the composition to thecure the antimicrobial coating.

In another embodiment, after heat sealing of the anodic layer, theanodic layer may be etched with an etching composition, to enable thesubsequently applied antimicrobial coating to better join with theremaining portion of the anodic layer. The etching composition,optionally in a solution form, may be applied to the web or sheet in avariety of manners, for example: by cascading the etching solution overthe web or sheet; by misting the etching solution over the web or sheet;by spraying the etching solution on the web or sheet; by dipping the webor sheet in the etching solution; and/or by rolling or brushing theetching solution on the web or sheet. Further optionally, heat ortemperature regulated air flow may be applied on the web or sheet toaffect the etching process.

The present disclosure provides a continuous web or sheet of anodizedaluminum including an antimicrobial coating that inhibits or preventsthe growth of microbes such as bacteria, mold, mildew, algae, fungi andyeast. When the continuous web or sheet is used to manufacturearchitectural materials and/or components that are frequently contactedby various users, it can reduce the spread of microbes, particularlypathogenic microbes, among those users.

These and other objects, advantages and features of the disclosure willbe more readily understood and appreciated by reference to the detaileddescription of the disclosure and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a process for manufacturing anantimicrobial anodized aluminum continuous web of the presentdisclosure;

FIG. 2 is a diagram of an antimicrobial composition suitable for usewith the present disclosure;

FIG. 3 is a diagram of the antimicrobial composition in another form;

FIG. 4 is a view of the antimicrobial composition bound to an anodiclayer of a continuous web of anodized aluminum; and

FIG. 5 is a schematic view of another process showing a pre-anodizedcoil product having an antimicrobial composition applied using secondaryapplication equipment.

DETAILED DESCRIPTION OF THE DISCLOSURE

I. Construction

The antimicrobial anodized aluminum product of the present disclosureincludes a continuous web (e.g., a substantial length of aluminum thatcan be pulled through multiple processing stations) or sheet having ananodic layer on one or both sides of the web or sheet.

To produce the anodic layer, a continuous web of raw aluminum core 70 isprovided and subjected to an electrolytic solution and anodizingenvironment. A variety of acids, such as sulfuric acid, oxalic acid,chromic acid, organic acid and/or phosphoric acid can be used to formthe anodic layer. The thickness of the anodic layer after anodizing canbe about 0 mils to about 0.400 mils, and preferably about 0.175 mils.

The anodic coating (aluminum oxide or Al₂O₃) layer 50 formed duringanodizing is porous. There are narrow holes in the aluminum oxide layerthat are about 100 Angstroms in diameter that extend from the top of apore to the bottom of the pore. When the web including the anodiccoating is placed in a bath of boiling water (e.g., in the sealingstation 6), water absorbs into the aluminum oxide, which in turn swellsthe aluminum oxide layer, substantially closing the pores. There also isa chemical reaction between the aluminum oxide and water, such thatAl₂O₃+H2O form a structure, 2*AlO(OH), which is called Bomite. The partof the aluminum oxide that has been converted to Bomite has less densitythan the part of the aluminum oxide layer that has not been hydrated bythe water.

The antimicrobial composition joined with the anodized layer can be ametal, such as silver, copper, and/or zinc that is coated and bound tothe anodic layer. Other suitable antimicrobial compositions areorgano-silanes. A suitable organo-silane, which is water based, is3-(trimethoxysilyl)propyldimethyl-octadecyl ammonium chloride), which iscommercially available from Nova BioGenetics, Inc., of Atlanta, Ga.,under the trade name BST AM500, and also commercially available fromAegis Environments of Midland, Mich. under the trade name Aegis MicrobeShield® AEM 5772 or AEM 5700. Organo-silanes that are similar incomposition to those available through Nova BioGenetics and Aegis canalso be used. The empirical formula for this compound is C₂₆H₅₈Cl N 03Si, and the molecular weight is 496.29. The structure of thisorgano-silane, shown as an active ingredient in a dilute aqueoussolution such as water or methanol, is illustrated in FIG. 2. Thestructure of this organo-silane, shown as an active ingredient in aconcentrate, is illustrated in FIG. 3.

With reference to FIG. 2, the organo-silane includes both across-linking or binding head 20 and a microbe inhibiting/destroyingtail 30. The tail 30 is capable of inhibiting/destroying a variety ofmicrobes, for example, bacteria, such as Escherichia coil andStaphylococcus aureus, as well as mold, mildew, algae, fungi and yeast.

The organo-silane of the present disclosure is used to form a coating onthe treated anodic layer 60 of the continuous web or sheet of anodizedaluminum. Specifically, with reference to FIG. 4, the organo-silane head20 performs two functions. In one, it attaches the surface of thetreated anodic layer 60 via short range Van der Waals and/or hydrogenbonding forces. In another, the head of one organo-silane molecule (asilanol group) reacts with another silanol group of an adjacentorgano-silane molecule and cross-links with it.

When applied to the treated anodic layer 60 in mass quantity, multipleorgano-silane silanol groups react and bind together and to the anodiclayer 60. Where other hydroxyl, amine or other substrate groups arepresent, the organo-silane molecule can join directly with thosemolecules or substrates as well. After the head 20 of each moleculebinds to the anodic coating, the antimicrobial head 30 remains exposedto form a nanocoating of the organo-silane antimicrobial on the surfaceof the anodic layer. This antimicrobial nanocoating can be of a depthfrom about 10 micrometers to about 40 micrometers, and preferably about20 micrometers.

II. Method of Manufacture

A method for producing an antimicrobial anodized aluminum product incontinuous web or sheet form will now be described with reference toFIGS. 1 and 4. With reference to FIG. 1, a continuous raw aluminum oraluminum alloy core web is introduced to the anodizing station 4 whereit is anodicly polarized in an electrolyte solution to form the anodiclayer. The web 2 continues to station 6 where it is heat sealed in asolution of hot water, at a temperature of about 205° F.

After the continuous web 2 is heat sealed, it continues to preheatingstation 8. At this station, the web is heat treated to a range fromabout 140° F. to about 200° F., preferably about 180° F. Before thisheat treatment, the temperature of the web is about 115° F. The heatersare stationed about 4 inches to about 10 inches from the web, preferablyabout 6 inches from the web, to exert the appropriate amount of heat toelevate the temperature of the surface of the web to the aforementionedranges. A suitable heater is a Chromalox ® S-RAD single element radiantheater, which is available from Chromalox, Inc. of Pittsburgh, Pa.Although shown with heaters on both sides of the web, one set of heaters(opposite the misted side of the web) optionally can be deleted fromstations 5 and 8.

After the web 2 is preheated, it continues on to pass the misters 7,which mist a coating of antimicrobial composition onto the surface ofthe anodic layer of the web 2 on one side of the web. Optionally, bothsides of the web may be misted as the application requires. The webpasses the misters at a speed from about 10 feet per minute to about 50feet per minute, preferably about 25 feet per minute. The misters can bespaced about 3 inches to about 10 inches, preferably about 7 inches awayfrom the web. The misters can also be spaced about 6 inches to about 10inches from one another (beside one another, across the web), andpreferably about 8 inches from one another.

The antimicrobial composition supplied through the mister can includethe organo-silane described above. That organo-silane can be dilutedbefore being applied by the misters. Specifically, the mixture of theantimicrobial composition can be about 3% to about 10%, preferably 3.4%to 6.8% and further preferably about 6.8% by volume Aegis AEM 5700;about 0.001% to about 2%, preferably about 0.1% by volume Dow CorningQ2-5211 Superwetting Agent (commercially available from Dow ComingCorporation of Midland, Mich.); and about 90% to about 99%, preferablyabout 93.1% high purity RO water.

The antimicrobial composition can be applied through the misters atabout 4 psi with an application from about 0.1 milliliters to about 0.8milliliters, preferably about 0.3 milliliters, per nozzle per squarefoot of the continuous web 2. The total application rate for all thenozzles on the continuous web is a range from about 1.5 milliliters toabout 2.5 milliliters per square foot of the web. As noted above, whenthe antimicrobial composition is organo-silane and it is applied to thesurface of the web, it hydrogen bonds to the surface of the anodiclayer, and the heads of the organo-silane cross-link to one another.FIG. 4 illustrates on a molecular level the interaction of theorgano-silane molecules with one another and the anodic layer to form anantimicrobial nanocoating on the anodic layer.

After the antimicrobial composition is sprayed to one side of the web,the continuous web 2 passes a first post-heating station 5. This stationcan apply heat to the web to keep the temperature of the web an elevatedrange from about 140° F. to about 200° F., preferably about 180° F. Ator near this station, the aqueous carrier, for example the water andmethanol, begin to evaporate. Depending on the application rate, a thirdpost-treatment heater 3 can be included in the system to furtherevaporate the water from the web and/or other volatile carriers from theantimicrobial composition.

The continuous web, now coated with an antimicrobial coating asdescribed above, can be processed using conventional techniques, androlled or cut for further distribution.

EXAMPLE 1

An example of preparing a antimicrobial composition and applying it to acontinuous web of anodized aluminum will now be described.

An antimicrobial composition was prepared by adding 1285 milliliters ofthe organo-silane Aegis AEM 5700 to an aqueous carrier having 17696milliliters of RO water and 19 milliliters of Dow Corning Q2-5211Superwetting agent to produce the resulting antimicrobial composition.The resulting antimicrobial composition was placed in liquidcommunication with the mister station 7.

Next, a continuous web 2 was anodized and heat sealed. The surfaces ofthe web 2 were heated to approximately 180° F. at preheating station 8.The anodized web 2 was fed past the antimicrobial treatment station 7 ata rate of about 25 feet per minute. The misters applied 2 millilitersper square foot of the antimicrobial solution to the passing web 2. Thepassing web was subjected to a post-heating at station 5 where the webwas heated again to about 180° F., where substantially all of the waterand methanol were evaporated off the web 2, and substantially all of theorgano-silane remained to form an antimicrobial nanocoating over theanodic layer 60. Further post-treatment heating was performed at station3.

A sample of the completed web 2 was then tested for its antimicrobialproperties. Specifically, the sample was subjected to JIS 2801-2000:Static Surface contact: Japanese Industrial Standard: Antimicrobialproducts—Test for antimicrobial activity and efficacy and ASTM E2149-01,“Standard Test Method for Determining the Antimicrobial Activity ofImmobilized Antimicrobial Agents Under Dynamic Contact Conditions,” ASTMInternational, which are hereby incorporated by reference. The resultsof the test on the sample produced in this example indicated a 99.99%reduction in staphlococcus aureus, which indicated that theantimicrobial anodized aluminum product of the present disclosure hadexceptional antimicrobial properties.

I. First Alternative Embodiment

An alternative embodiment of the present disclosure will now bedescribed. In this alternative embodiment, after the continuous web 2 isheat sealed, and before it continues to preheating station 8, it issubjected to an etching composition that lightly etches the sealed,anodic layer. “Etching” is a chemical treatment whereby an etchingcomposition is applied to and partially or fully dissolves or removes asealed layer or an anodic film or layer on an anodized aluminum surfaceto create a roughened morphology. An “etching composition” can be anyalkaline or acidic media capable of dissolving or removing all or aportion of aluminum oxide to a substantial degree, including but notlimited to sodium hydroxide, calcium hydroxide, phosphoric acid,hydrofluoric acid, sulfuric acid, bromic acid and chromic acid.

A “roughened morphology” refers to a condition where the heat sealedlayer or anodic film of the anodized aluminum includes an extended orprotruded surface area, which provides many sites for an increasednumber of mechanical—and in some cases chemical-bonds between the heatsealed layer or the anodic layer and an antimicrobial compositionapplied over the heat sealed layer and/or anodic film. The roughenedmorphology may resemble the surfaces depicted in FIGS. 1 and 2, or otherconfigurations depending on the etching solution applied, the durationof application and the temperature.

The etching composition may be a solution of water or other suitableliquid mixed with an alkaline, acidic or other caustic material, capableof dissolving and or removing the heat sealed layer and/or aluminumoxide layer. One etching solution is a solution of sodium hydroxide fromabout 0.1 to about 0.5 molar. Optionally, sodium hydroxide solutionsfrom about 0.5 to about 1.5 molar, and 1.0 to about 4 molar may also beused. Alternatively, the etching solution may be a solution ofphosphoric acid in concentrations of optionally about 0.1 to about 5.1molar, further preferably about 0.5 to about 3.0 molar and even furtherpreferably about 0.75 to about 1.5 molar. Solutions of sulfuric acid mayalso be used, however, the temperature and duration of time required tosufficiently dissolve an aluminum oxide layer must be significantlyincreased relative to the temperature and duration required with sodiumhydroxide solutions and phosphoric acid solutions.

The pre-etched heat sealed layer and anodic layer can be greater than0.1 mils (thousandths of an inch) or about 2.54 microns in depth. Due tothe etching, at least a portion of the heat sealed layer and the anodiclayer are removed so that a newly created bonding layer remains, wherethat bonding layer includes a roughened morphology. In this morphology,the bonding layer may be about 1 to about 20 nanometers, preferably 2 toabout 10 nanometers, and most preferably about 5 to about 6 nanometersin depth. Of course, the bonding layer can be of lesser proportions asdesired, for example, only 5%, 10%, 20%, 30% and/or 40% of the abovenoted depths, depending on the desired bonding of the antimicrobialcomposition to the remaining portion of the heat sealed and/or anodiclayers. Other roughened morphologies that increase the potential formechanical interlocking of the antimicrobial composition to the heatsealed and/or anodic layer can be used as desired, for example, thoseexplained in U.S. Pat. No. 7,029,597 to Marzak, filed Jul. 5, 2001,which is hereby incorporated by reference in its entirety.

After the etching composition is applied to the web or sheet, and thedesired bonding layer created, the web or sheet can be pre-heated atstation 8, and processed as set forth in the embodiment above to applythe antimicrobial composition as desired.

EXAMPLE 2

Another example of preparing a antimicrobial composition and applying itto a continuous web of anodized aluminum will now be described.

An antimicrobial composition was prepared by adding 136 milliliters ofthe organo-silane Aegis AEM 5700 to an aqueous carrier having 1864milliliters of RO water to produce the resulting antimicrobialcomposition. The resulting antimicrobial solution was placed in allowedto hydrolyze for one hour, and was heated to 210 F. before samples wereimmersed in the solution.

A web of aluminum was anodized and heat sealed. Thereafter, the web wasetched to remove at least a portion of the heat sealed layer and theanodic layer of the web. The etching was performed with a solution of0.15M molar sodium hydroxide, at a temperature of about 80° F., rolledonto the web, and left in contact with the web for about 2 secondsbefore the solution was rinsed from the web. It is believed that theetching composition created a bonding layer of about 2 microns.Thereafter, one 4 inch×6 inch sample was removed from the web.

The sample was individually immersed in the antimicrobial solution forabout five minutes. Then the sample was rinsed with RO water and airdried. It is believed that substantially all of the organo-silaneremained to form an antimicrobial nanocoating over the bonding layer.Further, it is believed that this nanocoating should be sufficientlybonded to the bonding layer so that the resulting sample can withstandfurther processing, such as stamping, bending, and other physicalmodification, without the antimicrobial nanocoating flaking off from, orotherwise disengaging, the sample to preserve the antimicrobialproperties of the sample.

IV. Second Alternative Embodiment

Various other processing techniques are being tested to produce abonding layer to which the antimicrobial composition can join, andremain joined upon further physical modification of the web or sheet.Several of these processing techniques are described below. In the firstfour techniques, an antimicrobial composition was prepared by adding 136milliliters of the organo-silane Aegis AEM 5700 to an aqueous carrierhaving 1864 milliliters of RO water to produce the resultingantimicrobial composition. The resulting antimicrobial solution wasallowed to hydrolyze for one hour, and was heated to 210° F. beforesamples were immersed in the solution.

In the first technique, two samples of raw ClearMatt, available fromLorin Industries of Muskegon, Mich., and two samples of Alumaplus rawmetal, also available from Lorin Industries, were cleaned withphosphoric acid at a concentration of 4.5% for one minute each, thenrinsed with RO water. Next, the samples were caustic etched with sodiumhydroxide at a concentration of 38 g/l for one minute each, then rinsedwith RO water, and then dipped in the antimicrobial solution for fiveminutes to coat the surfaces of the samples with an antimicrobialcoating.

In the second technique, two samples of ClearMatt, available from LorinIndustries, were cleaned for one minute, rinsed, caustic etched withsodium hydroxide at a concentration of 38 g/l for one minute, rinsedagain, desmutted with nitric acid at a concentration of 8% for 15seconds, anodized for 2.5 minutes with 12 amps, rinsed yet again, anddried. The samples were then dipped in the antimicrobial solution forfive minutes to coat the surfaces of the samples with an antimicrobialcoating.

In the third technique, two samples of ClearMatt were cleaned, immersedin phosphoric acid at a concentration of 30% for four minutes. Thesamples were then dipped in the antimicrobial solution for five minutesto coat the surfaces of the samples with an antimicrobial coating. TwoAlumaplus raw metal finish samples were also processed using the sametechniques.

In the fourth technique, two samples of Alumaplus, available from LorinIndustries, were anodized after being cleaned for one minute inphosphoric acid at a concentration of 4.5% and bright dipped in nitricacid at a concentration of 3.5% for one minute. Then the samples weredipped in the Alumaplus dye tank, which includes Grey NLN from SpecialtyDye and Bronze 2LW from Clariant, at a concentration of 0.8 g/l and 0.25g/l, respectively, for one minute, then sealed with nickel and hotwater. Two more samples followed the same processing steps, except forthe sealing process of nickel and hot water. Four Clearmatt samples,available from Lorin Industries, were also processed in the same order.Two of these Clearmatt samples were sealed and two of them were not.

In a fifth technique, 1360 milliliters of AEM 5700 were added to a20-liter dye tank, which already included a dye solution having 16 gramsof Grey NLN dye and 5 grams of Bronze 2LW with the remaining volumebeing water. Two anodized samples were passed from the anodizing tankto, the dye tank, which included the Aegis chemistry. Then the sampleswere immersed into the nickel seal for one minute and the hot water sealfor five minutes.

In another embodiment a continuous web or sheet of pre-anodized aluminum40 is processed from a payoff spool 42 to a rewind spool 44, as shown,for example, in FIG. 5. During this process, the web of aluminum 40 isfirst heated by heaters at station 46 to a range from about 140° F. toabout 200° F., preferably to about 180° F. The heaters are stationedabout 8 inches to about 16 inches from the web, preferably about 12inches from the web.

After the web 40 is preheated, the web is passed under the applicationpoint 48. Application may include up to two Nordson Rotary Atomizer gunsapplying antimicrobial solution at a rate from about 1 oz/min to about 4oz/min. The web 40 passes the application point 48 at a speed from about7 feet/min to about 90 feet/min, preferably at about 25 feet/min. Theweb 40 is next heated by a second set of heaters at station 58. Thisstation can apply heat to the web 40 to keep the temperature of the web40 an elevated range from about 140° F. to about 200° F., preferablyabout 180° F. The heaters are stationed about 8 inches to about 16inches from the web, preferably about 12 inches from the web. At or nearthis station, the aqueous carrier, for example the water and methanol ofthe solution, begins to evaporate.

The above descriptions are those of the preferred embodiments of thedisclosure. Various alterations and changes can be made withoutdeparting from the spirit and broader aspects of the disclosure asdefined in the appended claims, which are to be interpreted inaccordance with the principles of patent law including the doctrine ofequivalents. Any references to claim elements in the singular, forexample, using the articles “a,” “an,” “the,” or “said,” is not to beconstrued as limiting the element to the singular. Any reference to “atleast one of X, Y and Z” refers to one or more of X, Y, or Z, but doesnot require that each of X, Y and Z be present.

The embodiments of the disclosure in which an exclusive property orprivilege is claimed are defined as follows:
 1. An anodizedantimicrobial aluminum that resists the formation of microbes on thesurface of the aluminum consisting of: aluminum in a continuous web orsheet form; an anodic layer positioned near a surface of the aluminum inthe continuous web or sheet form; a heat sealed anodic layer positionedto lie near the anodic layer; such that pores of the anodic layer aresubstantially closed; organo-silane molecules bound to the surface ofthe heat sealed anodic layer wherein the organo-silane molecules arecross linked with adjacent organo-silane molecules to form anantimicrobial coating; and wherein the organo-silane molecules are3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride.
 2. Ananodized antimicrobial aluminum that resists the formation of microbeson the surface of the aluminum consisting of: an aluminum substrate; ananodic layer of aluminum oxide formed on a surface of the aluminumsubstrate; wherein pores formed in the aluminum oxide have beensubstantially closed to form a sealed aluminum oxide layer over theanodic layer of aluminum oxide; organo-silane molecules bound to thesurface of the sealed aluminum oxide layer wherein the organo-silanemolecules are cross linked with adjacent organo-silane molecules to forman antimicrobial coating; wherein the organo-silane molecules are3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride.